1. Field of the Invention
This invention relates to a vulcanization process for a pneumatic tire and a mold used therefor and is advantageously applicable to the production of a pneumatic radial tire having a thin rubber gauge in a sidewall portion.
2. Description of Related Art
In the production of the conventionally general pneumatic radial tire wherein a gauge of a sidewall rubber in a sidewall portion exceeds 3 mm at substantially a position of a maximum tire width, when a green tire after the shaping is vulcanized in a vulcanization mold or so-called split mold comprising a tread ring comprised of plural segments reciprocatively moving in a radial direction, a pair of side portion rings and a bead portion ring, it is general that air remaining in the mold, and gases produced therein are discharged through many ventholes toward the outside of the mold. As a result, many spews formed in the ventholes remain in a product tire after the vulcanization.
According to the conventional technique, therefore, there are problems that the yield of rubber material is lowered by forming many spews and the cutting removal of the spews from the product tire increases the working number and further the spew-cut traces spoil the appearance of the tire.
Recently, it is attempted to decrease the rubber gauge of the sidewall portion under a requirement of reducing the tire weight. In this case, a sectional area of a path for flowing rubber is decreased in the vulcanization of the green tire and hence the flowing resistance of the sidewall rubber is increased to obstruct the smooth flowing of the sidewall rubber, so that the smooth discharge of air and the like in the mold toward the outside of the mold accompanied with the rubber flowing is obstructed to increase a fear of creating bares in the product tire. In order to prevent the occurrence of such a bare, it is required to arrange the ventholes in the mold as large as possible and hence there is caused a problem that it is obliged to form much more spews.